This application is based upon and claims the benefit of Japanese Patent Application No. 10-156042, filed on Jun. 4, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a heat exchanger and a method of manufacturing the same with adhesive for securing a sealing property between a tube and a tank.
2. Description of the Related Art
A heat exchanger typically has tanks for accommodating heat medium therein, and plural tubes coupled with radiation fins and connected to the tanks through core plates. Specifically, end portions of the tubes are inserted into connection holes provided in the core plates, and joined thereto. After that, the core plates are attached to the tanks. The core plates and the tubes must secure a sufficient sealing property at joining portions therebetween for preventing leakage of the heat medium therefrom. Conventionally, the core plates and the tubes have been brazed to one another with the sufficient sealing property.
Recently, methods other than brazing for joining the core plates and the tubes have been proposed to rationalize the manufacturing process. For instance, mechanical processing such as crimping is carried out to produce pushing force between outer circumference surfaces of the tubes and the connection holes of the core plates so that the tubes are joined to the core plates by the pushing force. The mechanical joining method described above, however, easily produce minute clearances at the joining portions to lessen the sealing property. Therefore, this method requires a countermeasure for improving the sealing property.
To solve this problem, JP-U-61-18986 proposes a method in which sealing agent such as adhesive is applied to the joining portions after the mechanical joining is carried out. However, the sealing property cannot be sufficiently improved only by applying the sealing agent. It was confirmed by an immersion test that the joined core plates and the tubes dipped into an engine cooling water were separated from one another in a short period of time.
The present invention has been made in view of the above problem. An object of the present invention is to provide a heat exchanger having a core plate and a tube joined to each other with a sufficient sealing property and a method of stably and easily manufacturing the same.
According to the present invention, a heat exchanger has a tank for accommodating a heat medium therein, a core plate fixed to the tank and having a connection hole, and a tube having an end portion fixedly inserted into the connection hole of the core plate. The tube and the core plate are made of one of aluminum and aluminum alloy, and are mechanically joined to each other at a joined portion thereof. Further, an adhesive is disposed on a specific region of the joined portion through a wettability improving film interposed therebetween for improving a wettability of the adhesive to the specific region.
The wettability improving film makes the adhesive securely adhered to the joined portion therethrough. Specifically, because the wettability improving film has a good wettability to the adhesive, the adhesive can fill minute concave portions of the specific region even when surface roughness of the specific region is large. As a result, the sealing property between the tube and the core plate is improved.
The tube and the core plate can be mechanically joined to each other with the specific region covered with the wettability improving film. The wettability improving film may be formed before or after the tube and the core plate are joined to each other. After that, the adhesive is formed on the specific region through the wettability improving film.
The wettability improving film may be formed by jetting out a solution onto the specific region, and be formed by dipping the specific region into a solution. Accordingly, the heat exchanger can be easily and stably manufactured with a high sealing property.